The present invention relates generally to methods and systems for performing biometric identification of unknown individuals or verifying the identity of an individual utilizing optical spectral data from tissue. More specifically, the invention relates to methods and apparatus for biometric identification or verification of a living individual using optical energy in the near-ultraviolet, visible or near-infrared regions or combinations of wavelengths from these regions to measure the absorption and scattering of the light energy by tissue below the epidermis. The spectral features imposed by tissue on an incident optical radiation are unique to an individual and suitable for biometric determinations. Such determinations are made by using multivariate classification techniques to compare current tissue spectra with previously stored tissue spectral data contained in an enrollment database.
Biometric identification describes the process of using one or more physical or behavioral features to identify a person or other biological entity. There are two common modes in which biometric identification occurs: one-to-many (identification) and one-to-one (verification). One-to-many identification attempts to answer the question of, xe2x80x9cdo I know you?xe2x80x9d The biometric measurement device collects a set of biometric data from a target individual. From this information alone it assesses whether the person was previously enrolled in the biometric system. Systems that perform the one-to-many identification task such as the FBI""s Automatic Fingerprint Identification System (AFIS) are generally very expensive (several million dollars or more) and require many minutes to detect a match between an unknown sample and a large database containing hundreds of thousands or millions of entries. The one-to-one mode of biometrics answers the question of, xe2x80x9care you who you say you are?xe2x80x9d This mode is used in cases where an individual makes a claim of identity using a code, magnetic card, or other means, and the device uses the biometric data to confirm the identity of the person by comparing the target biometric data with the enrolled data that corresponds with the purported identity.
There also exists at least one variant between these two modes. This variant occurs in the case where a small number of individuals are contained in the enrolled database and the biometric application requires the determination of only whether a target individual is among the enrolled set. In this case, the exact identity of the individual is not required and thus the task is somewhat different (and often easier) than the identification task described above. This variant might be useful in applications where the biometric system is used to secure an expensive, dangerous, or complex piece of machinery. In this example, only authorized people should be able to use the equipment, but it might not be of interest to determine specifically which of the authorized personnel are using it at a particular time.
Although in general the one-to-many identification task is more difficult than one-to-one, the two tasks become the same as the number of recognized or authorized users for a given biometric device decreases to just a single individual. Situations in which a biometric identification task has only a small number of entries in the authorization database are quite common. For example, biometric access to a residence, to a personal automobile, to a personal computer, to a cellular telephone, to a handgun, and other such personal devices typically require an authorization database of just a few people.
Biometric identification and verification are useful in many applications. Examples include verifying identity prior to activating machinery or gaining entry to a secure area. Another example would be identification for matching an individual to records on file for that individual, such as for matching hospital patient records when the individual""s identity is unknown. Biometric identification is also useful to match police records at the time a suspect is apprehended, but true identity of the suspect is not known. Additional uses of biometric identification or verification include automotive keyless start and entry applications, secure computer and network access, automated financial transactions, authorized handgun use, and time-and-attendance applications.
Current methods for biometric identification are manifold, but some of the most common techniques include fingerprint pattern matching, facial recognition, hand geometry, iris scanning, and voice recognition. Each of these technologies addresses the need for biometric identification to some extent. However, due to cost, performance, or other issues, each of the existing methods has advantages and disadvantages relative to the other technologies.
One present biometric product on the market is known as the LiveGrip(trademark), made by Advanced Biometrics, Inc. This product is based on the technology disclosed in U.S. Pat. No. 5,793,881, by Stiver et al. In this patent, Stiver et al. disclose an identification system that is a security device, which consists of a cylindrical or elongated transparent shell with an internal light source and a means to scan the hand of the person grasping the shell to record the internal structure or subcutaneous structure of the hand using an imaging methodology. The system uses near-infrared light to image the pattern of blood vessels and associated tissue in the hand. The LiveGrip(trademark) product based on this patent is claimed to have reduced the ability for an intruder to fool the biometric system, as they claim can be easily done using a latex mold with many finger print readers or hand-geometry systems. However, the imaging approach requires good quality optics and/or detector arrays that add to both system complexity and cost. Further, the system relies on imaging blood vessels, and therefore, requires that the same site be presented to the system in use as during enrollment and further requires that the repositioning of the site is accurate enough to allow the software to align the two images to confirm identity. Finally, the size of the sensor head is limited to the portion of the hand that must be imaged for accurate identification.
Living human tissue is recognized as a dynamic system containing a multitude of components and analyte information that is particularly useful in the medical profession for diagnosing, treating and monitoring human physical conditions. To this end, effort has been directed toward developing methods for non-invasive measurement of tissue constituents using spectroscopy. The spectrographic analysis of living tissue has been focused on the identification of spectral information that defines individual analytes and relates such spectral data to the analyte""s concentration. Concentrations of these analytes vary with time in an individual person. Acquiring tissue spectral data with sufficient accuracy for use in diagnosis and treatment has proven difficult. Difficulties in conducting the analysis have been found that are related to the fact that the tissue system is a complex matrix of materials with differing refractive indices and absorption properties. Further, because the constituents of interest are many times present at very low concentrations, high concentration constituents, such as water, have had a detrimental impact on identifying the low level constituent spectral information and giving an accurate reading of the desired constituent concentration. Development of these techniques has always focused on the changes in spectral output with change in concentration of a dynamic analyte of interest, such as glucose. The techniques disclosed are focused on identifying concentrations of specific analytes, the concentration of which is expected to vary with time.
Improved methods and apparatus for gathering and analyzing a near-infrared tissue spectrum for an analyte concentration are disclosed in commonly assigned U.S. patent applications and issued patents. U.S. Pat. No. 5,655,530 and U.S. Pat. No. 5,823,951, filed Apr. 18, 1997, entitled xe2x80x9cMethod for Non-invasive Blood Analyte Measurement with Improved Optical Interfacexe2x80x9d relate to near-infrared analysis of a tissue analyte concentration that varies with time, with a primary focus on glucose concentrations in diabetic individuals. The methods and apparatus include placing a refractive index-matching medium between a sensor and the skin to improve the accuracy and repeatability of testing. U.S. patent application Ser. No. 09/174,812, filed Oct. 19, 1998, entitled xe2x80x9cMethod for Non-Invasive Blood Analyte Measurement with Improved Optical Interface,xe2x80x9d now U.S. Pat. No. 6,152,876, discloses additional improvements in non-invasive living tissue analyte analysis. The disclosure of each of these three applications or patents are hereby incorporated by reference.
U.S. Pat. No. 5,636,633 relates, in part, to another aspect of accurate non-invasive measurement of an analyte concentration. The apparatus includes a device having transparent and reflective quadrants for separating diffuse reflected light from specular reflected light. Incident light projected into the skin results in specular and diffuse reflected light coming back from the skin. Specular reflected light has little or no useful information and is preferably removed prior to collection. U.S. Pat. No. 5,935,062, filed Jun. 9, 1997, entitled xe2x80x9cImproved Diffuse Reflectance Monitoring Apparatusxe2x80x9d, discloses a further improvement for accurate analyte concentration analysis which includes a blocking blade device for separating diffuse reflected light from specular reflected light. The blade allows light from the deeper, inner dermis layer to be captured, rejecting light from the surface, epidermis layer, where the epidermis layer has much less analyte information than the inner dermis layer, and contributes noise. The blade traps specular reflections as well as diffuse reflections from the epidermis. The disclosures of the above patent and application, which are assigned to the assignee of the present application, are also incorporated herein by reference.
U.S. Pat. No. 5,435,309 relates to a system for selecting optimal wavelengths for multivariate spectral analysis. The use of only one wavelength gives insufficient information, especially for solutions having multiple components. The use of too many wavelengths can include too much noise and lead to combinatorial explosion in calculations. Therefore, the number of wavelengths used should be limited and the wavelengths well chosen. Genetic algorithms are used in this reference to select the most fit wavelengths. The disclosure of this patent is incorporated herein by reference.
The present invention includes methods and apparatus for biometric identification or verification of individuals using optical spectroscopy in the near ultraviolet, visible or near-infrared spectral regions and combinations of those spectral regions. The methods and apparatus disclosed provide superior performance relative to current biometric systems as well as provide other advantages. Prior art biometric identification devices have the distinct disadvantage of requiring the use of specific body parts in order to achieve their techniques. For example, fingerprint devices require that only the extreme ventral portion of the fingers can be used as the biometric site. The methods and apparatus of the present invention enable biometric identification to occur with finger, palms, wrists, forearms and other convenient sites on the body. Further, even in the case of using fingers, the present invention allows use of multiple sites along the finger on both the dorsal or ventral surfaces. Present finger print readers require that the same finger be presented to the reader for identification or verification that was presented during the enrollment analysis. The present invention can use different fingers (or other sites) for enrollment and for subsequent verification. This capability provides for increased enrollment efficiency since the user only has to present one enrollment site to the system, but also provides critical flexibility during the use of the device. An example of this flexibility is the case where the user has enrolled a site on a particular hand and that particular site is unavailable for subsequent analysis due to some injury or some severe surface contamination of the site. This spectroscopic-based biometric system of the present invention can operate on the site from the other hand without previous enrollment of such site. Further, although the results below are based on optical systems that require contact with the skin surface, the optical system such as that disclosed in U.S. Pat. No. 5,636,633 or U.S. Pat. No. 5,935,062 discussed previously could be used in the present invention to generate similar data in a non-contact mode. Such a non-contact biometric sensor apparatus would have significant advantages when installed in public locations to minimize wear and contamination issues associated with critical optical elements.
The present invention is based on applicant""s recognition that the resultant tissue spectrum of a particular individual includes unique spectral features and combinations of spectral features that can be used to identify the individual once the analytical device has been trained to identify the individual. The apparatus of the present invention performs biometric analysis using near-ultraviolet, visible, very near-infrared, or near-infrared energy and combinations thereof. In particular, the applicants have been able to demonstrate that the near infrared spectral data in the range from 1.25-2.5 xcexcm as collected with a near-infrared spectroscopic system can be used for spectral biometric determinations of identity or verification of identity. As well, the applicants have also shown that near-ultraviolet, visible and very near-infrared spectral data in the range from 350-1000 nm can also be used to perform biometric determinations. Although either or both of the aforementioned spectral regions can be used, the latter region may be advantageous due to the lower cost and generally higher performance of the silicon detectors that can be incorporated in systems operating in this spectral region.
In order to use the present invention for biometric tasks, the device and the algorithms need to be constructed to optimize performance in this application. Applicants have been able to achieve high accuracy rates with the techniques disclosed herein, even though the tissue being analyzed is a dynamic system with analyte concentrations, and thus, tissue spectral data, varying considerably over time and between analysis. Success of the method of the present invention is believed tied to at least two components.
First, the method incorporates an apparatus and technique for accurately and repeatably acquiring a tissue spectrum that minimizes effects due to instrumental, environmental and sampling changes, while remaining sensitive to slight changes in the spectral properties of tissue at any given wavelength. The system optimizes optical throughput both into and out of the tissue sample. Second, because the spectral features or combinations of spectral features that are unique for a particular individual are not readily apparent or identified by visual comparison of a spectral result, the present invention relies on discriminant analysis techniques to first train the device to identify spectral features of significance for the individual and then compare such features to new spectral data at the time of attempted identification or verification. The present invention incorporates discriminant analysis methods such as those based upon Mahalanobis distances, spectral residual magnitudes, K-nearest-neighbor methods, or linear or nonlinear discriminant techniques to compare spectral data acquired from an individual with spectral data present in a database.
The present invention, thus, includes a method for identifying or verifying the identity of an individual using non-invasive tissue spectroscopy. Depending on the tissue site and the wavelength range, the spectral data may be collected in a transmission or reflectance configuration. A preferred method and apparatus illuminates skin with selected radiation and collects the reflected, non-absorbed selected radiation. Diffuse, rather than specular, reflected light is preferably collected, more preferably light diffusely reflected from the dermis and deeper tissue rather than the epidermis. The spectral data collected can be stored in a computer database.
There are three major data elements associated with the present invention: calibration, enrollment and target spectral data. The calibration data are used to establish spectral features that are important for biometric determinations. This set of spectral data consists of series of tissue optical spectral data that are collected from an individual or individuals of known identity. Preferably, these data are collected over a period of time and a set of conditions such that multiple spectra are collected on each individual while they span nearly the full range of physiological states that a person is expected to go through. As well, the instrument or instruments used for spectral collection should also span the full range of instrumental and environmental effects that it or sister instruments are likely to see in actual use. These calibration data are then analyzed in such a way as to establish spectral wavelengths or xe2x80x9cfactorsxe2x80x9d (i.e. linear combinations of wavelengths or spectral shapes) that are sensitive to between-person spectral differences while being insensitive to within-person effects as well as instrumental effects (both within- and between-instruments) and environmental effects. These wavelengths or factors are then used subsequently to perform the biometric determination tasks.
The second major set of spectral data used for biometric determinations are the authorized or enrollment spectral data. Enrollment spectra are collected from individuals who are authorized or otherwise required to be recognized by the biometric system. Enrollment spectra can be collected over a period of seconds or minutes. Two or more optical samples can be collected from the individual to ensure similarity between the samples and rule out a sample artifact in one of the samples. If such an artifact is found, additional enrollment spectra can be collected. These spectral data can either be averaged together or otherwise combined, or stored separately. In either case, the data are stored in an enrollment database. In most cases each set of enrollment data are linked with an identifier for the persons on whom the spectra were measured. In the case of an identification task, the identifier can be used for record keeping purposes of who accessed the biometric system at which times. For a verification task, the identifier is used to extract the proper set of enrollment data against which verification is performed.
The third and final major set of data used for the spectral biometric system is the spectral data collected when a person attempts to use the biometric system to identify them or verify their identity. These data are referred to as target spectra. They are compared to the appropriate enrollment spectrum or spectra using the classification wavelengths or factors determined from the calibration set to determine the degree of similarity. If the target and enrollment spectra are sufficiently similar, the biometric determination is made. If the similarity is inadequate, then the biometric determination is cancelled and a new target measurement may be attempted. In the case of identification, the system compares the target spectrum to all of the enrollment spectra and reports a match if one or more of the enrolled individual""s data is sufficiently similar to the target spectrum. If more than one enrolled individual matches the target, then either all of the matching individuals can be reported, or the best match can be reported as the identified person. In the case of verification, the target spectrum is accompanied by a purported identity that is collected using a magnetic card, a typed user name, a transponder, a signal from another biometric system, or other means. This identifier is then used to retrieve the corresponding set of spectral data from the enrollment database, against which the biometric similarity is made and the identity verified or denied.
In one method of verification, principle component analysis is applied to the calibration data to generate spectral factors. These factors are then applied to the spectral difference taken between a target spectrum and an enrollment spectrum to generate Mahalanobis distance and spectral residual magnitude values as similarity metrics. Identify is verified only if the aforementioned distance and magnitude are less than a predetermined threshold set for each. Similarly, in a preferred method for biometric identification, the Mahalanobis distance and spectral residual magnitude are calculated for the target spectrum relative to each of the database spectra. Identify is established as the person or persons associated with the database spectra that gave the smallest Mahalanobis distance and spectral residual magnitude that is less than a predetermined threshold set for each.
One system for performing biometric tasks includes: a computer having an input device and an output device; a database including selected tissue spectral data for enrolled persons; a radiation or light source for projecting selected radiation into sub-epidermal tissue; a sampler to interface with tissue; a spectrometer including a detector for measuring subcutaneous radiation intensity over a plurality of wavelengths; and a classification program running in the computer for assessing the degree of similarity between a plurality of optical spectra by applying a set of classification factors. The program can include software for performing discriminant analysis. As well, the program can include a separate module to collect additional authorized spectral data or to remove existing spectral data from the database. In the case of using the spectral biometric system for verification tasks, the system will also include some means of establishing the purported identity of the person attempting to gain access. Methods to collect the purported identity include, but are not limited to, magnetic cards, PIN code, keyboard entry of the name or ID, voice command, transponder, etc.
These and various other advantages and features of novelty which characterize the present invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the object obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter in which there are illustrated and described preferred embodiments of the present invention.